This application relates to opto-electronic devices and techniques of using such devices to process signals.
Signals at frequencies below the optical spectral range, such as signals in the radio frequency (RF) and microwave spectral ranges, may be generated by using opto-electronic oscillators (OEOs) which include at least one closed loop with an optical loop section and an electrical loop section to generate a desired oscillation signal. In the optical section, an optical carrier is modulated to carry the oscillation signal below the optical spectral range. Some examples of OEOs are described in, e.g., U.S. Pat. No. 5,723,856 to Yao and Maleki, U.S. Pat. No. 5,777,778 to Yao, U.S. Pat. No. 5,929,430 to Yao and Maleki, and U.S. Pat. No. 6,567,436 to Yao, Maleki, and Ilchenko. In these examples, an OEO includes an electrically controllable optical modulator and at least one active opto-electronic feedback loop that comprises an optical part and an electrical part interconnected by a photodetector. The opto-electronic feedback loop receives the modulated optical output from the modulator and converts it into an electrical signal to control the modulator. The loop produces a desired delay and feeds the electrical signal in phase to the modulator to generate and sustain both optical modulation and electrical oscillation when the total loop gain of the active opto-electronic loop and any other additional feedback loops exceeds the total loss. Such OEOs use optical modulation to produce oscillations in frequency spectral ranges that are outside the optical spectrum, such as in the RF and microwave frequencies. The generated oscillating signals can be tunable in frequencies and can have narrow spectral linewidths and low phase noise in comparison with the signals produced by other RF and microwaves oscillators. Therefore, OEOs are hybrid devices that combine optical and electronic components and allow for versatile applications.
Signals in RF or microwave spectral ranges can be reconditioned, and processed with electronic circuits for various applications. For example, an electronic regenerative filter may be used to receive a microwave or RF signal and to regenerate a new signal at the same signal frequency with a reduced bandwidth and higher quality factor than the original signal. As another example, an electronic regenerative divider may be used to regenerate a signal at a new frequency of f/N where N is an integer representing the dividing factor of the divider. These and other electronic devices for processing RF or microwave signals have various limitations in part due to the electronic nature of such devices.